FIELD OF THE INVENTIONThe present invention relates principally to a method of detecting clogging of an air filter and to a system for ventilation, heating and/or air conditioning of a motor vehicle employing such a method.
BACKGROUND OF THE INVENTIONIt is usual to filter the air brought in by a system for ventilation, heating and/or air-conditioning of a passenger compartment of a motor vehicle by making the air pass through an air filter. Particles, especially dust particles, are retained by the air filter which finally becomes clogged, that is to say that it induces significant losses of pressure head reducing the throughput of air passing through the filter, and thus lowers the performance of the ventilation system. The clogging of the filter depends on the size and on the quantity of particles deposited on this filter. Hence, the rapidity of the clogging depends, in very large part, on the conditions of use and especially on the quantity of dust in the air at the time when the heating, ventilation and/or air conditioning system is used.
It is therefore desirable to be able to detect the state of clogging.
Consequently one object of the present invention is to offer a method of detecting filter clogging which is easy to implement.
It is also an object of the present invention to offer a method of detecting filter clogging avoiding false alarms.
It is also an object of the present invention to offer a method of detecting filter clogging employing few special-purpose electronic components.
It is also an object of the present invention to offer a reliable method of detecting filter clogging.
SUMMARY OF THE INVENTIONAccording to a first aspect of the present invention there is provided a method of measuring clogging of an air filter of a system for ventilation, air conditioning, and/or heating of a passenger compartment of a motor vehicle, the method comprising:
a) starting up an air-pumping device including an electric motor driving an air-driving rotating aerodynamic component;
b) measuring a characteristic value of the electric motor driving at least one rotating aerodynamic component for driving the air passing through the filter the clogging of which is being measured, in order to obtain a measurement value;
c) comparing the measurement value with at least one calibration value in order to deduce therefrom a measure of the clogging of the filter.
The method of the present invention may employ the measurement of the strength of the current drawn by an electric drive motor of the air-circulation blower in the system for ventilation, air-conditioning and/or heating of the passenger compartment of a motor vehicle. For example, during a first step, a calibration is carried out. This calibration may be a measurement taken with a new filter. In a case in which the recirculated air is not filtered, it is possible to carry out an acquisition of a calibration value, for example by acquisition of a calibration current ieof the electric motor corresponding advantageously to the ventilation of the passenger compartment of the vehicle by recirculation of the air taken in from this passenger compartment without filtering.
For a measured current i of less than the calibration current iemultiplied by a constant coefficient of less than 1, taking the various corrections into account as appropriate, the filter is considered to be clogged and an alarm is triggered, for example in the form of the display of a light signal.
According to a second aspect the invention provides an installation for ventilation, air conditioning and/or heating of the passenger compartment of a motor vehicle employing the method of the first aspect, the installation including an air filter, air-pumping means including an electric motor driving a rotating aerodynamic component for driving the air, means for measuring a characteristic value of an electric motor driving at least one rotating aerodynamic component for driving the air passing through the said filter in order to obtain a measured value, and means for comparison with a calibration value in order to generate a clogging indication such as an alarm.
The said comparison can be carried out by the computer of the air-conditioning system. The installation may include a means of obtaining the calibration value by measurement of a characteristic value of the electric motor driving at least one rotating aerodynamic component for driving air not passing through the filter, for example recirculated air.
BRIEF DESCRIPTION OF THE DRAWINGSThe invention will be better understood by means of the description below and of the attached FIGURE, given by way of non-limiting example, and which is a diagrammatic view of an embodiment of a system according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTIn FIG. 1 can be seen, represented diagrammatically, a system for ventilation, heating and/or air-conditioning of the passenger compartment of a motor vehicle. The ventilation system represented includes an outside-air intake1 which is filtered by adust filter3 and anon-filtered intake5 allowing ventilation by recirculation of air originating from the passenger compartment. A flap7, advantageously motorized by amotor9, makes it possible, under the control of acomputer10, to open the outside-air intake1 or, in contrast, theintake5 for the air originating from the passenger compartment. The air is driven by an air-pumping device11 such as a blower including a propeller, a turbine, vanes or the like, driven by an electric motor controlled by acircuit13 which is itself controlled by thecomputer10. Afirst heat exchanger15 and/or asecond heat exchanger17 make it possible to modify the temperature of the air. Aflap19 makes it possible, on demand, to orient or not to orient the air towards theexchanger17.
Adistribution flap21 allows distribution of air between the various air outlets in the passenger compartment, for example between afirst outlet23 at windscreen level allowing for de-icing/de-misting, asecond outlet25 at the level of the head of the occupants of the passenger compartment, and athird outlet27 situated in the region of the feet of the occupants of the passenger compartment.
Ventilation systems also exist in which the filter is arranged downstream of the air-intake flap, and in this case the recycled air as well as the outside air is filtered.
The present invention is based on the revelation that the clogging of thefilter3, reducing the flow of air driven by theblower11, alters the operating conditions of the motor, and, for example, reduces the strength of the electric current drawn by the motor of this blower and its speed of rotation.
Advantageously, a measurement of a reference current is taken. Advantageously, the reference current is measured under the same conditions ofblower11 motor performance, of temperature and of passenger-compartment leaktightness. Advantageously, the measurements are carried out when the passenger compartment is isolated, that is to say when the doors and windows are closed and the vehicle is at rest, that is to say when its speed with respect to the outside air is zero or substantially zero.
The first method of clogging detection can be employed whether the filter is arranged upstream (see FIG. 1) or downstream of the air-intake flap. It consists in comparing the electric current passing through the electric motor for driving the blower with a reference value measured with a new filter. This method is based on the principle that the clogging of the filter generates an additional loss of pressure head on the air circuit of the treated air, which causes a lowering of the electric current which passes through the said motor. The best precision of this measurement is obtained when it is carried out under the same conditions as the reference measurement, that is to say, at identical vehicle speed and with identical air distribution in the vehicle (air blowing all cold, de-icing all hot, etc.), with the same windows open and at the same temperature of the windings of the motor, which depends on the outside temperature, on the operating time of the electric motor and on the torque which it has to overcome. That being so, this method applies rather to a confirmation for maintenance attention by the garage with a vehicle at rest, the electric motor operating for a given time and with a given air distribution.
A second method, which can be used in the case in which the filter is situated upstream of the air-intake flap7, makes it possible to generate an instantaneous calibration value, independent of the state of clogging of the filter. The calibration value and the measurement value are produced within a very short space of time, which makes it possible to ensure that these two measurements are taken under the same conditions of distribution, of airspeed of the vehicle, of outside temperature and of motor temperature. Moreover, the obtaining of an instantaneous calibration value makes it possible to take into account the aging of the electric motor. The order in which the calibration value and measurement value are obtained is unimportant. According to this second method, a first measurement is taken, for example, the flap7 ensuring that theintake5 is closed and theintake1 is open. In this case, thefilter3 induces no loss of pressure head in the ventilation circuit, which makes it possible to measure a calibration value by measurement of a characteristic value of the motor of theblower11 such as the strength of the current drawn, for example, for a given power supply voltage, equal for example to 12 volts, a voltage measurement across a resistor placed in series with this motor, the speed of rotation of this motor or the like. The value of the measurement which constitutes a calibration value is stored in memory, by thecomputer10 for example.
Under the control of acomputer10, the flap7 swings so as to close theintake5 and to open theintake1. A measurement is taken of a characteristic value, such as the current drawn by the motor of theblower11 etc., for example, in order to obtain a measurement value.
When the ratio between the measurement value and the calibration value falls below a predetermined threshold, possibly adjustable by the driver, thecomputer10 actuates an alarm such as apilot lamp29, for example, placed on the instrument panel.
The presence of wind is not troublesome, since it tends to increase the throughput through the aeration apertures and to increase the current drawn by the motor of the blower. In the worst case, a clogged filter will be regarded as serviceable, but it will be detected at the next measurement in the absence of wind, which is not troublesome since the clogging of a filter progresses slowly.
It is possible, for example, in the course of step6, to calculate a clogging index equal to the ratio of the current drawn by the motor of theblower11 when theintake1 is open, divided by the strength of the current flowing in the motor of theblower11 sucking air into a new filter (first method) or else through the recirculated-air intake (second method). This current strength is a constant for a vehicle and is stored in memory-storage means of thecomputer10. The variation in the percentage reduction of the air throughput of a filter with the reduction in the clogging index is an affine function. For a new filter, the clogging index is equal to 1 and the reduction in the throughput is equal to 0, whereas for the reduction in the throughput of 40% with respect to that of a new filter, the clogging index is equal to 0.9.
In the context of the second method, it is possible to be independent of the measurement conditions by calculating a clogging index known as “normalized” index, equal to the ratio Ic=[(current drawn by the motor of the blower in fresh-air position of the current filter)/(current drawn by the motor of theblower11 in air-recirculation position (current measurement)]/[(current drawn by the motor of the blower in fresh-air position of the new filter)/(current drawn by the motor of theblower11 in air-recirculation position (factory measurement)].
Advantageously, for one or other of these two methods, the measurement of the clogging of the filter is taken upon start-up after the doors have been closed and before any windows have been opened.
In a variant, the measurement of the clogging is taken by the after-sales department. A measurement according to the first method is particularly suitable for ventilation systems including air-conditioning appliances which are unregulated and/or which lack means9 for driving the flap7. The flap can be actuated manually, or a first measurement can be taken in order to obtain a measurement value, the filter being in place and the second measurement can be taken in order to obtain a reference value, the filter being removed or the filter being replaced by a new filter. The characteristic value of the motor of theblower11 is determined by measurement means incorporated into the vehicle or, advantageously in this case, by separate measurement means.
The present invention is extremely simple to implement and of low cost. The measurement of the current can be made by employing a resistor used to govern the consumption of the motor of the blower. In a variant, a Hall-effect sensor is used, allowing a more accurate measurement but at a higher cost.
For the user, provision is made to display an alarm, for example, a pilot lamp on the instrument panel representing the fact that the clogging of the filter is exceeding a defined threshold.